Fused couplers are important passive components in fiber optic communication systems, and perform functions such as light branching and splitting in passive networks, wavelength multiplexing/de-multiplexing, filtering, polarization selective splitting and wavelength independent splitting.
Fused couplers are formed traditionally by joining two or more independent optical fibers in which the claddings of the fibers are fused over a small region. The devices work as a result of energy transfer between the optical fiber cores on the basic principle of coupling between bi-conically tapered optical waveguides.
Critical in the manufacture of fused couplers, such as those disclosed in U.S. Pat. Nos. 5,175,782, 5,339,374 and 5,644,666, is the need to arrange the various fibers precisely during the fusing process. Specifically, optical fibers or optical fiber preforms are mechanically grouped into an array to control the mechanical geometry of the optical cores in the fibers while heating to fuse them in a biconical taper structure. The biconical taper structure has a down taper and an up taper formed by pulling with tension on the grouped fibers or preform bundle while controlling the heating and cooling cycle. Mechanical control of the geometry of the optical cores while fabricating the biconical taper structure is difficult, yet critical. Holding the fibers in a precise arrangement is especially difficult as the number of fiber increases. This difficulty increases the complexity of equipment used in manufacturing fused couplings and results in increased waste owing to the inevitability of occasionally failing to maintain such precise fiber arrangement.
Therefore, a need exists for a simplified method of producing fused optical couplings. The present invention fulfills this need among others.